The present invention relates to thrombosis filters. To be more specific, it is about removable thrombosis filters which can be securely fixed at a selected location in the vascular system for trapping blood clots, and removed when desired such as when no longer required.
In recent years, pulmonary embolism has become an increasingly common medical emergency. Pulmonary embolisms may be caused by venous thrombosis that in turn may be caused by blood flow retention, venous intimal damage or coagulation abnormalities. Emergency or prophylactic treatments for these conditions include anticoagulant therapy, thrombolytic therapy, thrombectomy and inferior vena cava blocking procedures.
Among these therapeutic options, when an inferior vena cava blocking procedure is selected, one option is to perform a laparotomy under general anesthesia during which the inferior vena cava is ligated, sutured and shortened, or clipped. Another option is to intravenously insert a thrombosis filter into the inferior vena cava under local anesthesia. A laparotomy however, requires general anesthesia and is susceptible to thrombosis formation due to the discontinuation of anticoagulant therapy prior to surgery. For these reasons, percutaneous filter insertion is now more widely employed since it requires only local anesthesia.
Blood is returned to the heart from the lower part of the human body through the inferior vena cava and from the upper part of the body through the superior vena cava. The neck vein, known as the jugular vein, leads to the superior vena cava which is a vein that enters the upper part of the heart. A percutaneously inserted catheter that extends through the jugular vein and the superior vena cava and then into the heart can be manipulated to exit the heart through the mouth of the inferior vena cava into the heart. The inferior vena cava, a vein that enters the lower part of the heart, can also be accessed through the patients femoral vein. Thus, the inferior vena cava can be reached through two endovenous routes, both of which are available percutaneously.
A currently used percutaneous filter is shown in FIG. 9. The filter has anchors, 43, at the end of six struts, 81, with a head or central hub or fixation part, 5. One example of how this filter is used is to lead the filter within a capsule with the head of the filter introduced first if using the transfemoral vein approach or with the tail of it introduced first if using the transjugular vein approach. This type of filter possesses hooks at the end of the struts that impinge the inner wall of the blood vessel in order to ensure its firm fixation at the time of insertion. It is released from the capsule and expands within the inferior vena cava where it function as thrombosis filter.
Filters of the type shown in FIG. 9 perform the desired filtering function, requiring only local anesthesia for insertion. This has contributed to the high usage of the filter. A filter of the type shown in FIG. 9 is disclosed in U.S. Pat. No. 4,817,600. Approximately two to three weeks after insertion of this type of filter, neointima grows around the filter and its anchors to the inner wall of the blood vessel, which becomes an obstacle to the removal of the filter after its function has been fulfilled. Furthermore, this filter was not designed or intended to be removed. Since the need for a thrombosis filter, in many patients, is temporary, it may be desirable to remove the filter when it is no longer needed. In the prior art devices, such removal can be preformed surgically which exposes the patient to the usual risk and trauma associated with surgery. Thus there is a need for a thrombosis filter that can be removed without surgery.
The subject invention fulfills the need of a medical filter which can be non-surgically removed even after neointima has developed. As a result of this invention, a medical filter has been developed which includes insertion and removal accessories that enable the goal to be achieved. The filter of this invention includes a filtering portion that is permeable to the blood flow but which will filter out emboli and thrombus and will also hold the filter firmly in a selected location and permit removal through an endovenous route. The filtering and holding device of this medical filter includes two filter units that face each other and do not have hooks that impinge the inner wall of the blood vessel, in the same manner as the prior art filters, in order to anchor the device in the blood vessel.
The objective of this invention, therefore, is to provide thrombosis filters with a favorable filtering function which can be securely anchored at a desired location and be removed through an endovenous route even after the growth of neointima.